Method of bleaching pulp



UNITED STATES PATENT OFFICE.

METHOD OF BLEACHING PULIP.

No Drawing.

As ordinarily practiced the bleachingof paper pulp is accomplished by treating the fibre with a bleaching agent, such as chlorine, chlorite, hypochlorite, sulfite, hyposulfite and potassium permanganate. Ofthemanyprocesses now in use the pulp in the bleaching system is of about the following mixtures: 3% fibre to 97% water up to about 8% fibre to 92% Water; thus the bleach is very materially diluted when it is brought in contact with the fibre.

My process enables the bleaching. to be accomphshed in a more dense mixture; as about 1820% fibre to 80-82 water. In this way I eliminate the customary loss of bleach by excessive dilution, as well as the loss of cellulose by long contact with the bleach.

In continuous bleaching systems, the bleach is in contact with the fibre for five to nine hours, ",in batch system the time is shorter.

My invention makes it possible to bleach the pulp in a considerably less time, usually from 7 to 15 minutes. By so doing the bleach is only in contact with the fibre for a sufiicient length of time to perform its function of bleaching, and will thus overcome the undesirable effect of overbleaching, and the subsequent loss of weight and strength of fibre.

My invention can be carried out with any suitable machinery, I prefer to collect the fibre on a vacuum filter covered with a fine wire cloth. When excess water is extracted by the vacuum the bleach is applied in a manner to be equally distributed over the pulp; the bleach having been previously heated to 170 0r 180 F. Sufiicient bleach and vacuum are applied to thoroughly saturate the entire mat of stock which remains in this condition long enough for the pulp to reach the desired color at which time the vacuum is again applied in order to remove the bleach and by pulling air through the mat of fibre the oxidizing efl'ect of the bleaching agent is facilitated.

Specification of Letters Patent.

Patented Mar. 14, 1922.

Application filed June 17, 1921. Serial No. 478,428.

When bleaching is completed the fibre can be washed with clean water in order to remove all traces of bleach, and organic compounds formed in the process of bleaching, that have a deleterious effect on highly bleached cellulose or other fibres. The bleaching agent may consist of any of the chemicals hereinbefore mentioned dissolved in water, the strength of the solution varying according to the agents used and the nat-ure of the material to be bleached.

The bleaching may be accomplished in one or two operations. That is half the quantity of bleach required to bleach the pulp may be added, when the strength of same is exhausted the pulp would be washed with clean water and then subjected to final bleaching by the second operation.

Having thus described the invention, what I claim is z- 1. The process of bleaching fibrous and cellulose material which consists in saturating the same with a bleaching agent and allowing the same to set until the required color has been imparted to the material, then passing air through the material to remove the bleaching agents and simultaneously facilitates its oxidizing effect.

2. The process of bleaching fibrous and cellulose material which consists in saturating the same with a bleaching agent and allowing the same to set until the required color has been imparted to the material, then subjecting the material to a vacuum orsuctlon action, whereby the bleaching agent is removed and air passed therethrough to facilitate the oxidizing action.

3. The process of bleaching fibrous and cellulose material which consists in-collecting the material on a vacuum filter to form a mat and remove excess moisture, then saturating the mat with a hot bleachin solution and allowing the same to set until the required color has been imparted to the material then subjecting the mat to a vacuum or suction action, whereb the bleaching agent is removed and air passed therethrough to facilitate the oxidizing action.

In testimony whereof I afiix my signature in presence of two witnesses.

GEORGE M. TROSTEL.

Witnesses Bnssm BORING, H. W Smut. 

